Patients with colorectal cancer that has spread to other parts of the body may benefit from a novel form of treatment, according to a recent study.

Researchers found that by adding the new drug, bevacizumab (Avastin, made by Genentech), to standard chemotherapy, more patients responded to treatment, and the responses tended to last longer than with chemotherapy alone. They reported their results in the Journal of Clinical Oncology (Vol. 21; 1: 60-65).

While the new treatment is promising, it is still in clinical trials at this time. Further studies are needed to establish its safety and effectiveness before it can be approved for use by the Food and Drug Administration (FDA).

Bevacizumab is not a normal chemotherapy drug. It is a type of manmade protein known as a monoclonal antibody. In the body, it attacks a substance known as vascular endothelial growth factor (VEGF), which normally helps new blood vessels form. It works not by killing the cancer cells themselves, but by attacking the tumor’s blood supply. This is known as antiangiogenesis therapy.

In order for tumors to grow larger than a few millimeters (about the size of a pencil lead), the cells that make up the tumor must have access to a blood supply. Cancer cells ensure this by secreting substances that cause new blood vessels to form.

Antiangiogenesis therapy is supposed to work by preventing these blood vessels from developing. But while antiangiogenesis agents have shrunk tumors in the lab, the results in cancer patients have been mixed.

Because of this, researchers are now testing them combined with chemotherapy, hoping that the combination may be more effective than either one alone, without being more toxic.

Standard treatment for metastatic colorectal cancer is chemotherapy, usually is in the form of a combination of the drugs 5-fluorouracil and leucovorin (5FU/LV), or 5FU/LV plus irinotecan.

For the present study, Fairooz Kabbinavar, MD, from the University of California Los Angeles, and colleagues wanted to see if adding bevacizumab to a standard chemotherapy regimen would improve the results.

They studied 100 previously untreated patients, with half receiving 5FU/LV alone and half receiving 5FU/LV plus bevacizumab (low-dose or high-dose).

People who received low-dose bevacizumab were more likely (40% vs. 17%) to have their tumors shrink than those who got only chemotherapy, and had a longer period of time before the tumors started to grow again (9 months vs. 5 months). They also appeared to live longer.

Those receiving the high dose of bevacizumab had results somewhere in between the other two groups.

There were, however, some problems associated with the new therapy. Those getting bevacizumab were more likely to experience serious blood clots, high blood pressure, and nosebleeds.

The study authors described their results as "preliminary" based on the small numbers of patients studied, and they noted that two larger studies now underway are nearing completion. Each will have close to 1,000 participants. As with this study, they are trying to determine if adding bevacizumab to standard chemotherapy regimens can improve responses to these agents.

The importance of these larger studies is demonstrated by a recent large study of bevacizumab in breast cancer patients. While early, smaller studies showed it to be promising, researchers recently reported disappointing results in the larger clinical trial.